I renamed a word in my save game directory and then tryed to launch it with minecraft open

I renamed my minecraft saved world to something else and i had minecraft open at the world select and selected the world that i changed the name of but in minecraft it was not changed.

What I expected to happen was...:
I expected the world to laad properly

What actually happened was...:
The game crash and gave me a crash report

Steps to Reproduce:
1. Open up minecraft
2. Go to world select
3.Open up your minecraft world save directory
4. rename a world
5. launch the world that you renamed.